http://www.cnbc.com/id/39863078
The above link discusses the inherent value of fine quality Iranian made carpets in terms of the materials used (i.e. 100% silk), knotting and level of detail, location, and age of the rug.
Rug collectors seek out various designs including qom, tabriz, kashan, nain, and isfahan carpets as these carpets usually appreciate in value over time.